1. Field of the Invention
The present invention relates to a toothbrush which is constructed of a bundle of bristles which is folded in a U-shape bend and set into a brush head with each bristle terminated in two different shapes at opposite ends.
2. Description of the Prior Art
There have existed toothbrushes that are adapted for use in tooth brushing with each user's own tooth condition or possibly disorder taken into consideration. For example, some toothbrushes have bristles of which end is terminated in a round shape to massage the gum; to prevent periodontitis or gumboil, some toothbrushes are equipped with bristles each of which is terminated into a tapered-off shape to remove bacterial plaque developed in a small groove (called periodontal pocket) between a tooth and the gum. Most of these toothbrushes are developed with a view to achieving a single purpose, and have thus the corresponding advantage only.
Since health care for the teeth and the gums catches today's health oriented public's attention, there is a need for a toothbrush which has a plurality of functions. To meet such a need, a toothbrush having two types of bristle end shapes has been developed. For example, Japanese Utility Model Open Gazette No. Sho-57-50220 has disclosed such a toothbrush. This toothbrush is provided with two types of bristles, one terminated in a tapered-off shape at its end and the other type having no such taper at its end. Since the tapered end projects further than the other type, the tapered ends are put into contact with the teeth and gums in advance of the other ends and easily reach the periodontal pockets.
Generally speaking, compared to the bristles terminated in other shape, taper ended bristles are subject to deformation. Due to its small elasticity, the taper ended bristle exhibits poor recovery characteristics. This problem may be improved by using thermoplastic polyester as a material of the bristles, to some extent. However, tapered ends of the bristles remain free to be inserted into the periodontal pockets, this aggravates deformation of the bristles. Only a short-time of use is sufficient to keep tapered ends of the bristles deformed. Such a deformed toothbrush provides an adverse effect to the teeth and the gums rather than providing desirable brushing effect to the gums.